CA1044127A - Pneumatic radial tire - Google Patents

Abstract

Abstract of the Disclosure An improved belt construction for a radial or semi-radial tire comprising a reinforcing belt layer includ-ing helically formed filaments is disclosed. Between main belt layers is interposed an intermediate reinforcing layer composed of a reinforcing element formed of helically formed filaments each having a tensile breaking strength of at least 140 kg/mm2 and elongation at tensile breaking strength of at least 1.2 times the smallest elongation at tensile breaking strength of the cords of the main belt layers. The intermediate reinforcing layer as a whole is extensible and compressible.

Description

This invention relates to pneumatic radial tire and more particularly to an improved belt construction for a radial or semi-radial tire comprising a carcass including cords arranged in parallel or substantially parallel with the vertical center sectîon through the rotational axis of the tire and a belt arranged in a tread o-f the tire and having an excellent rigidity in circumferential direction of the tire.
The term radial tire and semi-radial tire usually called in pneumatic tire techniques shall be understood to mean a tire construction comprising a carcass composed of one or a plurality o cord fabric plies and extending from one o-f beads to the other bead, cords of each ply being arranged in parallel or subs~antially parallel with the '! - ,: .
vertical center section through the rotational axis of the -~
tire, that is, located at a radial or substantially radial plane of the tire.
The radial tire comprises a reinforcing belt --; interposed between the carcass and the tread and usually -composed of single or a plurality of rubberized cord fabric -,~ . . layers without including weft threads.
Each rubberized layer of the belt is usually ~`ormed of inextensible material, for example, a steel cord, glass fiber and the like9 these cords in the rubberized layer being extended in parallel with each other and inclined at a small angle to the circumferential direction of the tire.
i It is no exaggeration to say that abilities of the radial tire, that is, a cornering property, resistance to wear, anti-skid property and cut resistant property thereof -~

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Measures of obtaining the rigidity in the circum-ferential direction of the belt is mainly consist of the use ; of the above mentioned inextensible material and the cord angle which is small to the circumferential direction of the tire.
On the one hand, the larger is the tire in size the higher rigidity of the belt construction i.s required.
In order to satisfy such requirement, use is made of inex--~ tensible material ha~ing particularly high tensile rigidity ., such as a steel cord, etc. This is because of the fact that the material ha~ing a small rigidity requires a large number o-f belt plies to be used thus increasing the total thickness of the belt, and as a result, small heat accumulation inhierent to the radial ~ire becomes degraded. In a tire for trucks, buses or construction vehicles, if the carcass is formed into the radial construction, tires are used to be confronted with an important problem that requires to increase -the cut resistant property. For this purpose, use is made of ma~erial having a high tensile rigidity such as a steel cord, etc. When such kind of radial tire runs on road at a high speed5 a tire failure is started from belt ends, particularly from those belt ends which are inclined at a ~ -small angle to the circumferential direction of the tire, thereby inducing a separation failure between adjacent belt layers.
` Such separation failure is caused by brea~age of the tire occurred due to its heat accumulation and mechanical , ~, - , , .. .. . ., . -- . . . . . -.
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' ' , ' ! . ~ . ~ ` , fatigue and developed into a tire failure.
When the tire runs on road, the heat accumulation therein becomes remarkably increased at both ~he belt and the tread which are large in thickness.
In addition~ the largest mechanical strain occurs at those belt ends which are in contact with soft rubber.
Particularly, an interlayer shearing strain is produced between the belt layers crossed with each other at a small angle to the circumferential direction of the tire.
The amount of such interlayer shearing strain is considerably large. The wider the width of the belt layer or the smaller the cord angle of the belt layer to the circumferential direction or the larger the rigidity of the belt cord is, , the larger the amount of the interlayer shearing strain is ;, 15 produced. The measures of decreasing the amount of the .,, "
interlayer shearing strain is contrary to the measures of increasing the rigidity of the belt necessary for obtaining the characteristics of the radial tire. It is a difficult problem to harmonize the high rigidity of the belt with the excellent characteristics of the radial tire for those ' skilled in tire design field.
`! i An object of the invention, therefore, is to ,, ~ . - , l obviate the above mentioned drawbacks which have been ! encoun~ered with the prior art techniques.
Another object of the invention is to provide a radial construction tire comprising a belt formed of an i~ inextensible material such as a steel cord, etc., which can reduce separation failure produced when the tire runs on road at a high speed under a heavy load çondition without deteriorating a cut resistant property, resistance to wear ,. . . .
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and steering property inherent to the radial cons~ruction tire and which has an excellent durability.
A Eeature of the invention is the provision of a pneumatic radial tire comprising a reinforcing belt layer including helically formed filaments, comprising a carcass including cords arranged in parallel or substantially parallel with the vertical center section through the rotational axis of the tire and a belt interposed between ~ :
said carcass and a tread and including a.t least two main :
layers having cords formed of inextensible material such as a steel cord, etc., said cords being inclined at a small angle along two directions crossed with respect to the circumferential direction of the tire, the improvement comprising an intermediate reinforcing layer interposed between said main belt layers and composed of at least one rubberi~ed layer including reinforcing elements spaced apart ~j-from each other and embedded therein, said reinforcing layer ` beîng formed of a helically formed filament or a bundle of a plurality o:f helically formed filaments each -formed of material having a tensile breaking strength of at least 140 kg/mm2, said reinforcing elemen~s having an elongation ~ -at tensile breaking strength of at least 1.2 times the :~ .
smallest elongation at tensile breaking strength of the ~ .
cords of said main belt layers, said intermediate reinforc- -ing layer as a whole being extensible and compressible.
:; The invsntors have investigaked what is the : mechanism of producing the breakage of the belt ends and the ~ :
method of improving the durability of a radial tire comprising ~ . :
: :a belt including inextensible cord such as a steel cord~
:~ 30 etc. and reinforcing a tread portion when it runs on road at -~
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a high speed under heavy load.
The invention will now be described with reference to the accompanying drawings, wherein:
Fig. 1 is a diagrammatic transverse section through a tire illustrating accumulated heat temperature distribution;
Fig. 2 is a graph illustrating a relative displace-ment of a belt cord produced when the tire shown in Fig. 1 - is inflated by applying a normal internal pressure therein;
Fig. 3a is a diagrammatic transverse section through a tire illustrating deformation of a belt produced when the tire is subjected to a load; ~-: :,Fig. 3b is a graph illustrating strain produced when a cord angle of the belt shown in Fig. 3a is changed;
Fig. 4 is a graph illustrating interlayer shearing strain as a function of positions between the belt layers;
Fig. 5a is a front elevational view of a helically formed filament;
, j, Fig. 5b is its sectional view through an outer contour projected on a plane perpendicular to the axial direction of one pitch of the ~ilament shown in Flg. 5a; ~ - -Fig. 6 is a graph illustrating a relation between a force subjected to a reinforcing element according to the ,~
invention, conventional steel cord and nylon cord and an elongation produced in these element and cord;
Fig. 7 is a graph illustrating a compression ,~ modulus of elasticity of rubberized rein-forcing element ~ , according to the invention and rubberized conventional steel , cord compared with that of rubber;
Fig. 8 is a graph illustrating retained tensile strength of the reinforcing element according to the invention ,:

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obtained in the case that strains repeatedly occurred therein and that of the conventional steel cord;
Fig. 9 is a diagrammatic transverse section through an embodiment of the tire according to the invention;
Fig. 9A is a graph illustrating interlayer shearing strain at various positions between belt layers of the tire according to the invention as compared with that of the conventional tires; and Figs. 10 to 13 are diagrammatic transverse sections through various modified embodiments of the tire according to the invention.
It has been well known that the mechanism o~
producing the breakage of the b01t ends is due to heat accumula~ion and mechanical fatigue of the tire.
In Fig. 1 is shown a temperatwre distribution produced near a belt of a tire for construction vehicles having a size of 18.00 R33 when the tire runs on road at a speed o;E 20 km/hour under a load of 14.85 tons. As seen from Fig. 1, the highest temperature is present at that portion of the belt which is located near a point which is 1/4 the tread width measured -from the shoulder of the tire.
Strains produced at various portions o:E the belt -layer will now be described.
A mechanical strain is produced when an internal ~ -~
pressure is applied in a tire and when the tire is subjected to a load. When the internal pressure is applied in the tire, the belt layer is subjected to tension on the one hand and a shearing strain is produced between the belt layers on ~ the other hand.
;; 30 The rubberized belt including cords inclined at an ':

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angle to the circumferential direction is subjected to tension, and as a result, its rigidity is increased. In other words, the shearing strain produced between the belt layers and the strain produced between the cord and rubber function to maintain the belt position against the internal pressure applied iIl the tire.
This fac~ will clearly be understood by the following equation given by ... ..

:;, .', '~, where ~ is a shearing stress, ~ is a shearing strain and E i;~
is a modulus of elasticity. -In Fig. 2 is shown a relative displacement in the circumferential direction of the belt cord produced when a normal in~ernal pressure of 6.3 kg/cm2 is applied in a radial construction tire for construction vehicles having a size of 18.00 R33.
The belt is composed of 5 layers lB, 2B, 3B, 4B
and 5B in the order as mentioned from the carcass side, the cords of the layer lB being inclined at 60 toward right upwardly to the circumferential direction, the cords of the layer 2B being inclined at 23 toward right upwardly to ~he circumferential direction, the cords of the layer 3B being inclined at 23 toward left upwardly~ the cords o-f the layer 4B being inclined at 23 toward right upwardly and the cords ~ .
of the layer 5B being inclined at 23 toward left upwardly.
The term right and left shall be understood to mean the ..~
~ direction of the cords. The cord is formed of a conventional , steel cord. ~

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The tensile strength of the cords of the layers lB
to 3B are large, while the tensile strength of the cords o-f the layers 4B and 5B is small.
As seen from Fig. 2, the largest relative displaoe-ment in the circumferential direction of the belt layers lB, 2B, 3B, 4B and 5B and hence the largest interlayer shearing strain occurs between the layers 2B and 3B corresponding to the main belt layers whose cords have the highest rigidity.
` In Figs. 3a and 3b is diagrammatically illustrated how strain is produced when the tire is subjected to load.
As shown in Fig. 3a, in general, the tire tread has at its crown a radius of curvature C in expectation of a uniform wear. It is a matter of course that if the tire is subjected to the load, the ground contact surface of the tire becomes fIat. In this case, a belt b embedded therein in substan-tially parallel with the radius of curva$ure C of the crown , is deformed into flat as shown by dotted lines.
'! This deformation causes the belt b to deform from ;l~ its arcuate shape shown by full line into linear shape shownby dotted lines so as to be stretched from X by A in the ~
;l axial direction of the tire. As a resul~, the cord angle of -.
the belt is changed to produce strain as shown by dotted ~lines in Fig. 3b. As seen from Fig. 3b, the largest strain occurs at the belt end. ;i -i;
In Fig 4 is shown a relationship between the ; interlayer shearing strain and position between belt layers -~
when a radial tire having a size of 18.00 R33 is subjected to a load of 9.9 tons. ~ -~ : , As seen from Fig. 4, the interlayer shearing ~; 30 strain becomes maximum at a position between the belt layers ~,.; :~ : ,-~", ~ ~ ::- .
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ZB and 3B in the same manner as in the case when the tire is inflated by applying the internal pressure therein. In fact 9 it has been found out that a separation failure occurs between the belt layers 2B and 3B on the road test of the tire thus rendering the tire useless and waste.
In order to alleviate the maximum interlayer shearing strain, the following measures, etc. have been proposed.
(1) The cord angle of both the belt layers 2B and 3B
is made large.

(2) The cords of both the belt layers 2B and 3B are ~ made small in diameter and rigidity.
; ~3) Rubber sandwiched between the belt layers 2B and 3B is made large in thickness.
All of these measures~ however, have led to reduction of the rigidity of the belt and enlargement of the outer diameter of the tire, thereby degrading the resistance to wear, safe steering ability, etc. of the tire and hence deteriorating the ability inherent to the radial tire. As a result, ît is not desrious to apply the above mentioned measures to the tire.
The inventors have investigated on methods of alleviating the maximum interlayer shearing strain without ~ -involving the above mentioned dïsad~antage and led to the ;~
following conclusions.
That is, the maximum interlayer shearing strain can be alleviated by inserting a cord having an excellent strain absorbing property into a space formed between the main belt layers where the maximum interlayer shearing strain occurs. In this case~ it is meaningless to use an '~ '' '' , , ,, , . . , ~ .

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inextensible reinforcing element such as a steel cord used for a conventional belt. Because, the use of such inexten-sible reinforcing element results in occurrence of an interlayer shearing strain in a space formed between a layer inclusive of such inextensible reinforcing element (such layer will hereinafter be called as an intermediate rein-forcing layer) and the belt layer.
The intermediate rein-forcing element is required to be deformed in itself so as to alleviate the interlayer shearing strain produced between the main belt layers.
The inventors have investigated on material and ` construction having the above mentioned property and recog-nized that a helically formed filament described in U.S.
; patent specification No. 3,682,222 has such ability.
This helically formed filament has property and ` construction to be described later. The inventors have ` found that an optimum combination of a main belt layer formed of inextensible material such as conventional steel cord, etc. and an intermediate reinforcing layer formed of a helically formed filament provides a radial tire which can make its belt significantly durable wi~hout impairing the advantage inherent to the radial tire.
That is, in accordance with the invention, in ~-order to provide such radial tire, a rubberized cord layer constituting a main belt layer is formed of inextensible cords such as a conventional steel cord and between these maln belt layers is inserted an intermediate reinforcing layer formed of a helically formed filamen~ having excellent extension and compression properties.
~` 30 The proper~y of the helically formed filament is -' ~--, .

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closely associated with the belt material and required to :
satisfy ~he following relationship.
The rigidity of belt in the circumferential direction of the tire - The shearing strain produced between the belt layers in the absence o-f the intermediate reinforcing layer = The shearing strain produced between the main belt layers ~A) ~ Deformation of the intermediate reinforcing element formed of a bundle of helically formed filaments (B).
If the bundle of the helically formed filaments is small in its resistance to deformation and hence easily deformable, stress produced therein becGmes small to increase the shearing strain (A), and as a result, it is impossible to expect alleviation of the interlayer shearing strain.
On the one hand, if the resistance to deformation ; ;
of the intermediate reinforcing element B becomes excessively large, the intermediate reinforcing layer B is not deformed, so that the interlayer shearing strain produced between the ~ :
intermediate reinforcing layer and the main belt layer becomes increased.
Inventors' investigations have yielded the result ,. .
that the helically formed filament may be formed of steel or .~:
any other less extensible metals or glass or organic materials, that the helically formed filament formed of material such ~ :
as nylon or rayon whose tensile breaking strength is on the ..
,~ order of 80 to 110 kg/mm2 does not reveal the ability of the intermediate reinforcing layer, and that the helically formed filament formed of mater.ial whose tensile hreaking strength is at least 140 kg/mm2, preferably at least 170 kg/mm2 .' ., ~ .
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can attain the object of the invention.
The carcass body of the radial tire according to the inven~ion is of so-called radial or semi-radial construc-~ion and composed of at least one rubberized ply containing cords embedded therein and formed of steel, metal or organic textile, the cords being arranged in parallel with or inclined at a small angle to the vertical center section ; through the rotational axis of the tire.
The belt arranged between the carcass and the tread is composed of at least two main layers each composed of a rubberized cord layer containing cords embedded therein ~ ;~
and having a tensile breaking strength of at least 190 kg/mm2 and elongation at tensile breaking strength of at most 5S~
, the cords being inclined at an angle of at most 30 to the circumferential direction of the tire.
Between the main belt layers is arranged the ., ,~ ,: .
intermediate reinforcing layer composed of helically formed filaments Before describing the configuration, construction and ef:Eect of the intermediate reinforcing layer, the con-s~ 20 figuration and construction of the helically formed filament according to the invention will now be described. ~;
In accordance with the invention, one or a plurality of, preferably 2 to 50, more preferably 3 ~o 30 of flexible ~ - -and permanently helically formed relatively thin filaments ., , ~, ~, each formed of material having a tensile breaking strength of a value within the above mentioned range and a filament ~;
diameter of 0.1 mm to 1.0 mm, preferably 0.13 mm to 0.5 mm l~ are assembled together without twisting at random and I without winding an exterior binding wire thereabout into a cord wh-ich is used as a reinforcing element.

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In Fig. 5a is shown the configuration of the helically formed filament and in Fig. 5b is shown an outer contour projected on a plane perpendicular to the axial direction of one pitch of the filamen~ shown in Pig. 5a, the -~ 5 filament being shown in section. It is ideal to make ~he outer contour shown in Fig. 5b true circle for the purpose of uniformly distributing tension subjected -to the element.
But 7 it is technically very difficult to make the outer contour of the filament true circle. In addition, a number of steps are required to incorporate the filament into the tire, so that i~ is still further difficult to maintain such -true circle-shaped outer contour o-f the filament in the tire product.
; Experimental tests and investigations on practically ;
allowable degree of deviation of the outer contour of the filament from the true circle have demonstrated that if a ratio of the maximum diameter Dmax of the outer contour projected on a plane perpendicular to the axial direction of one pitch of the above mentioned helically formed filament . .
to the minimum diameter Dmin thereof at any part of the tire crown portion lies within a range to be described later, the -~
tension subjected to the filament becomes practically substantially uniformly distributed ~hereon, and tha~ hence a premature fatigue failure of the tire is not induced.
That is, in Fig. 5b, a ratio of the maximum diameter Dmax to the minimum diameter Dmin, i.e. DmlX is required to lie from 1 to 1.5. In addition, the relationship between the average diameter D, i.e Dmax Dmin of th h li formed filament and the filamen-t diameter ~ has to sa-tisfy D>2~, preferably D>3~, more preferably 3~<D<15~.

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, It might be possible to presume that as a method of obtaining a desirous elongation of a filament formed of material havlng a high tensile breaking strength such as high carbon steel, a plurality of undulate filaments are arranged in one plane and spaced apart from each other.
In this case, however, tension is concentrated into bent portions of the undulate filament in response to extension or compression thereof. In addition, this tension is a bending tension that tends to be concentrated into one part in the filament section, so that a premature fatigue failure frequently occurs at these bent portions of the undulate filament. Thus, it is practically impossible to use such ~ -undulate filament in place of the helically formed filament.
If provision is made of the helically formed , filament in order to obtain any desired elongation, the tension occurred in response to the extension or compression -subjected to the filament in its lengthwise direction is substantially uni-formly distributed over any portion of the -filament in its lengthwise direction. In addition, such tension is a torsionaI shearing stress that tends to be ~-relatively uniformly distributed in the filament section, so --that it is possible to completely prevent the filament from being subjected to the premature fatigue failure.
` ''', The inventors' experimental tests and researches have yielded the following results. In the firs~ place, in ~ -order to prevent breakage o the filament due to fatigue, it ;
`~ is preferable to make the filament diameter ~ small. ;--~Secondly, in order to improve the cut resistant property of ~ ,. .: .
the ilament, the tensile strength per unit area of the - :~ -filament can be increased by reducing its diameter by drawing ~ :

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~ , , it, so ~hat it is preferable to make the filament diameter small.
But, if the filament diameter ~ is smaller than 0.1 mm, the filament becomes frequently cut in non-allowable recurrence in the step of helically forming the ^filament, and as a result, such small filament diameter is not econom-ical. On the contrary, if the filament diameter ~ exceeds 1.0 mm, internal stress produced in the -filament in the step of helically forming filament becomes excessive]y large. In addition, the torsional shearing force produced when the filament is subjected to extensible or compressive force in its lengthwise direction is concentrated into the outer contour portion of the filament. As a result, in order to provide the ~ilament having a tensile strength which is sufficient to resist the same exterior force as in the case , . . .
of the filament having a small diameter, ~he overall sectional area of the filament must be made large if compared with the small diameter filament, thereby requiring a much amount of material. As a result, such excessively large filament diameter is also not economical.
As can be seen from the above~ the filament diameter ~ should lie within the above mentioned range.
; The relationship between the filament diameter Oll the one hand and the average diameter D of the outer -~ 25 contour projected on a plane perpendicular to the axial direc~ion of one pitch of the filament on the other hand will now be described. If D is smaller than 2~, the pitch of the filament must be made excessively small for khe purpose of obtaining a desired elongation. In the same manner as in the case of making the filament diameter . .

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excessively small, the filament becomes frequently cut in non-allowable recurrence in the step of helically forming the filament. At the same time~ the internal scress produced in the step of helically formillg the filament becomes excessively large.
On the one hand9 a plurality o-f helically formed filaments are assembled together without twisting at random into a cord-shaped reinforcing element which is then arranged in the ti.re. In this case, a plurality of cord-shaped reinforcing elements are arranged in zigzag in the tire, so that if D is larger than 20~, the number o-f reinforcing elements must be made small for the purpose o~ maintaining a ~ -distance between the most protruded por~ions of the two adjacent reinforcing elements that required for a desired 1 15 separation resistant property of the tire. As a result, the reinforcing element does not function as the intermediate ~I reinforcing layer. On the contrary, if the number of rein-;' forcing elements is made large in order to make the rigidity l .
of the intermediate reinforcing layer high, the above . .
mentioned dis~ance between the two adjacent reinforcing elements could not be maintained, and as a result, the desired separation resistant property o the tire can no~ be expected.
In addition, in order to maintain the desired ~ -~
separation resistant property of the tire, not only a dîstance between the two adjacent reinforcing elements in . .
trans~erse direction thereof, but also a distance between ;
two superimposed main belt layers disposed on and beneath `:
one reinforcing element when such one reinforcing element only îs used as well as a distance between two adjacent ':
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reinforcing layers when such two reinforcing elements are used are required to be kept within a certain range. Such distance must be of one measured between the most protruded portions of the two adjacent reinforcing elements, so that it is always necessary to make a rubber layer large in thickness~ thereby impeding economy and degrading the rigidity of the belt. As seen from the above, the average diameter D of the helically formed filament must lie within the above mentioned range.
The pitch of the helically formed filament may suitably be selected in association with a modulus of ,~ elasticity of the ~ilament, filament diameter ~ and average ~:
diameter D of the outer contour projected on a plane perpen-dicular to the axial direction of one pitch of the filament - 15 such that the optimum elongation at ~ensile breaking strength and modulus of elasticity of the tire required for the use thereof are obtained.
The number of helically formed filaments to be assembled together without twisting at random into a cord-shaped reinforcing element should be smaller than 50. Ifthis number exceeds 50, the bundle diameter becomes exces-sively large even though the average diameter D ~f one helically ormed filament is small. The same problem occurs as was encountered when the ave~age diamerer D i9 excessively large. ~s a result, the number of helically formed filaments to ~e assembled together without twisting at random into a cord-shaped reinforcing element may suitably be selected within the above mentioned range by ta~ing into considera~ion a bala~ce between the cut resistant property required for the use of the tire and any other abilities and economy.

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.,, , : :, The relation between the force subjected to the reinforcing elements constructed as above described according to the invention and to a conventional stranded steel cord on the one hand and elongations produced in the element and cord on the other hand will now be described with reference to a practical example.
In Fig. 6 is shown tensile test results with the force in kg/cord or kg/bundle taken on ordinate and with the elongation in % on abscissa. Tn Fig. 6, a dotted lines curve ~ shows a tensile test resul~ yielded from a conven-tional steel cord having a strand construction of lx5, filament diameter ~ of 0.25 mm and cord diameter of 0.68 mm and full line curves ~ and ~ show tensile test results yielded rom reinforcing elements according to the invention.
~; lS The tensiIe test result shown by the full line curve ~ was , yielded from a reinorcing element composed of a bundle of 5 -~ilaments according to the invention each having a filament diameter ~ of 0.25 mm7 average dlameter D of an outer -cor~tour projected on a plane perpendicular to the axial direction of one pitch of the filament of 0-95 m]n~ b~=1.25, ~=3.8, and pitch of 10.5 mm. The tenslle test result shown ; by the full line curve ~ was yielded from a reinforcing ' element composed of 14 ilaments according to the invention each having a filament diameter of 0.175 mm~ average diameter `~ 25 D of an outer contour projected on a plane perpendicular to the axial direction of one pitch of the filament of 1.1 mm, =1.20, D~~6.3 and pitch of 11 mm. In Fig. 6, a dotted lines curve ~ shows a tensile test result yielded from a conventional nylon cord of 1,260 denier/2 strands. :.;
As seen from Fig. 6, the relation between the ` ,: ' ' ~:
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-force subjected to the intermediate reinforcing elements according to the invention and the elongation thereof shows that the elongation b within the proportional limit is larger than that of the conventional steel cord. That is, 5the elongation b o-f the intermediate reinforcing elements according to the invention when the elements are subjected to the small force a is larger than that of the conventional steel cord. This modulus of elasticity at the initial stage which is defined by ba in Fig. 6 is important for obtainin~
10 the e~tension and contraction characteristic of cords required for reducing the shearing strain to be produced when the cords are subjec~ed to the belt tension which is not always so large as to break the cords. The reinforcing element composed of a bundle of helically formed filaments ,;
15having a small diameter ~ is excellent in the above mentioned `, modulus of elasticity. It will ~e understood, therefore~
that such reinforcing element is ideal for attaining the object of the invention.
The use of the reinforcing element composed of a 20 bundle o-f helically formed filaments according to the invention ensures a signi~icant reduction of the compression modulus of elasticity of the reinforcing element.
The difference between the compression modulus of elasticity and compression fatigue property of the rein- -25forcing element according to the invention and those of the i~ conventional stranded steel cord used for the belt layer wlll now be described with reference to a practical example.
In Fig. 7 are shown compression test results. In ~ , ,.
Fig. 73 the compressive force in kg is taken on ordinate and 30the compressive strain in % is taken on abscissa. In this ~
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test, use was made of two test pieces, one of which being composed of a cylindrical rubber containing one conventional stranded steel cord embedded thercin and the other being composed of the same cylindrical rubber containing one reinforcing element formed o-f one bundle of helically formed filaments according to the invention embedded therein.
In Fig. 7, a dotted lines curve ~ shows the relation ~etween the compressive force in kg subjected to the conven-~ional stranded steel cord having a stranded construction of lx5, filament diameter ~ of 0.25 mm and coTd diameter of 0.68 mm and the compressive strain in ~ produced therein.
A full line curve ~ shows the relation between the compres-sive force in kg subjected to the rein-forcing element according -~
to the invention composed of 5 filaments each having a diameter ~ of 0.25 mm, average diameter D of an outer contour projected on a plane perpendicular to the axial direction of one pitch of the filament of 0.95 mm, ~ =1.25, D~=3.8 and pitch o-f 10.5 mm and the compressive strain in % produced therein. In Fig. 7, a dotted lines curve e shows the same re]ation with respect to a test piece formed of rubber only. -It is a matter of course that the rubber of all of these three test pieces is of the same rubber compound.
As seen -from Fig. 7, the compression modulus of ` elasticity of the reinforcing element according to the invention is extremely small and close to a value of the rubber specimen. ~ -:~ In Fig. g is shown a compression fatigue test result. A percentage of tensile strength after the fatigue test with that of a new tire, i.e. retained tensile strength in % is taken on ordinate and number of strains repeatedly ....

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occurred is ~aken on abscissa. In the present test, use was made of two test pieces, one being composed of a rectangular rubber body containing a plurality of conventional stranded steel cords embedded therein and the other being composed of the same rectangular rubber body containing a plurality of bundles o-f helically formed filaments according to the invention embedded therein~ and these two test pieces were subjected to 5% repeating compressive strain in an intermit-. ten~ manner. ' In Fig. 8, a dotted lines curve ~ shows the retained tensile strength as a function of the number of , strains repeatedly occurred for the conventional stranded !~ steel cvrd having a stranded construction of lx5, filament diameter ~ of 0.25 mm and cord diameter of 0.68 mm and a full line curve ~ shows a relati~n similar to the dotted lines curve a for the reinforcing element according ~o the ;
` invention composed of 5 filaments each having a filament diameter ~ of 0.25 mm, average diameter D of an outer contour , projected on a plane perpendicular to the axial direction of J 20 one pitch of the filament of 0.95 mm, Drm----1.25, D~=3.~ and pitch of 10.5 mm. As seen from Fig. 8, the retained tensile strength of the reinforcing element according to the invention is far superior to that of the conventional steel cord.
The configuration, construction and effect of the ~25 intermediate reinforcing layer composed of the reinforcing , : . - , . .
element shaped and constructed as above described according to the invention will now be described. ~ -As rubber which constitutes together wi~h the `
reinforcing elements of the intermedlate reinforcing layer, ~i ~ :
;~ 30 use may be made of a rubber compound having a Shore A hardness ., ': .

; .:
.
.- . . ~ . . .- . - . , ~ . . ~ .

of 50 to 85, 300% modulus of elasticity of 100 to 250 kg/cm2 and tensile breaking strength of 150 to 250 ~g/cm2, preferably a soft rubber having a large elongation and movable in response to ~he deformation of the reinforcing element.
More particularly, the use of rubber having a hardness and ~ -modulus of elasticity which are equal to or smaller than those of the coating rubber of the belt ensures a significant effect.
The reinforcing element of the intermediate rein-forcing layer is closely related to the cord angle of the main belt layers of the belt disposed on and beneath the ; intermediate reinforcîng layer, but is inclined at an angle ;~ of 15 to 75, preferably 18 to 70 with respect to the circumferential direction of the tire.
The intermediate reinforcing layer may be arranged near the belt ends only by taking the o~ject thereo into consideration. If 2 intermediate reinforcing layers are used, the reinforcing element of one of these layers may be crossed with the reinforcing element of the other layer with respect to the cir~umferential direction of the tire.
Alternatively, the cord angles of the two adjacent inter- , mediate reinforcing layers may be inclined in the same ;~
direction wi~h respect to the circumferential direction of .
i the tire. In this case, it is possible to effectively prevent separation failure of the tire caused by mechanical ~, . .
strain subjected thereto.
The property of the intermediate reinforcing layer `~
relates to the material and construction of the main belt layers disposed on and beneath the intermediate reinforcing layer. It is preferable to use a reinforcing element having ,."-.: , ,;.. ,;

an elongation at tensile breaking strength which is at leasc1.2 times, p-referably 1.5 times the smallest elongation at tensile breaking strength of steel cord used for the main belt layers, modulus of elasticity within proportional limit of at most 5xlO 3 kg/mm2, preferably at most 4X10 3 kg/mm2 and compression modulus of elasticity of a value which is smaller than 0.9 times, preferably smaller t:han 0.7 times the largest compressive modulus of elasticity of the steel cord used for the main belt layer. The term the modulus of elasticity within the proportional limit shall be understood to mean a value defined by ;` :
100 ' ~
where a is a tension in kg subjected to the cord or the reinforcing element within an elastic limit wherein the modulus of elasticity of the cord or reinforcing element can be restored, b is an elongation in % produced therein and S ~ :
is an effective sectional area in mm2 of the cord. -The width of the intermediate rein-forcing layer in its widthwise direction may be wider or narrower than the :~
width of the main belt layers disposed on and beneath .~;
thereof More particularly, the width of the intermediate reinforcing layer containing helically formed filaments embedded therein may be made e~ual to or wider than that the width o the main belt layers disposed on and beneath the intermediate reinforcing layer without involving the problem of increasing the shearing strain as in the case of using the conventional steel cord. In addition, in the case of using a bundle of a plurality of helically formed filaments, -~ " - ' .

~hese helically formed filaments are assembled together without kwisting at random contrary to the conventional steel cord formed of twisted filaments. As a result, it is possible to sufficiently penetrate the rubber into gaps formed between the filaments which mechanical bonding force can compensate for insufficient rubber-to-filament chemical bonding.
In addition~ if a rubberized layer containing steel cords inclined at a large angle with respect to ~he circumferential directlon of the tire or containing steel cords havîng a large elongation or small rigidity is inter-: posed as an auxiliary means between the intermediate rein-forcing layer and the main layer of the bel~, it is possible to effectively change the rigidity of the tire in a stepwise manner.
The helically formed filament constituting the reinforcing element o:E the intermediate reinforcing layer may be formed o-f a wire material having an excellent rubber-to-filament bonding property, particularly brass plated -;
; 20 steel filament and any other metal fibers, glass fiber or ; aromatic polyamide fiber having a high modulus of elasticity, etc. which can satisfy the above mentioned requirements.
The invention, therefore, is capable of providing a radial construction tire comprising a belt layer having an ; 25 excellent durability and high ability.
Effective embodiments of the pneumatic radial tire according to the invention will now concretely be described.
Example 1 In Fig. 9 is shown a vertical center section through the rotational axis of a pneumatic radial tire . . , - ~ ~- , :.- : : ..
:: . . . . .
. ~ : . , ~. , ''' ~ ` ."'. I` ,., ',,~ " '.','`, , :' ' : : : :: . :.:: : , :

according to the invention. The tire shown in Fig. 9 is of a steel radial tire for trucks and buses having a tire size of 10.00 R20 14PR. A carcass 1 composed of 1 ply formed of steel cords is extended from one of beads through a tire crown portion to the other bead in parallel with the vertical center sec$ion through the rotational axis of the tire. The carcass 1 is formed of usual steel cords.
; The steel cord of the carcass 1 has a tensile breaking strength of 170 kg/corcl. Both ends o the carcass 1 are wound around and secured to a pair of bead wires 2, respectively, to form turn-up portions 4. In order to further reinforce the bead portions, each bead wire 2 is urther wound by a chafer 3 composed of 1 rubberized nylon cord layer.
In addition, a bead filler 5 formed of hard rubber having a Shore A hardness of 80 is arranged in a space surrounded by the carcass 1, bead wire 2 and turn up portion ~ -4 of the carcass ply.
In a crown portion 6, a belt 9 composed of 4 layers inclusive of 1 intermediate reinforcing layer 8 is interposed between the carcass 1 and a tread 7. The belt 9 is composed o 4 layers lB, 2B, 3B and 4B arranged in the order as mentioned from the carcass side, the belt layer 3B
~; constituting the intermediate reinorcing layer 8 and the . .
other belt layers lB, 2B, 4B having construction shown in the ollowing Table.
~ .

'',~ ~ ' ~ .' , ,, :

' '~

-. . ., - - - : . . . - , . . ~ : . . , , . , , .. , ~, ............. . .

a~ ~~ ~ a ~4 ~ 4 .~ b4 ~ 1 .~-~-rJ. r~ ~
~1 hr-l S~ ~1~--I
~rl h~ ~ rl h ., ' ~) o ,~i: o ~ o O :,,., :"
t`l 1-) ~ ~
'~' ~ ." ' ', ,: .
rl-~ ~ '' ~ U~-rl ~o ,': td ~ , o\ _ _ S: ~ h :.
':~ ~ ~ ,' ~
' ___~ ',' ', ~ ~ '' '~
D rl~ ~ bO :,' ,' .
,_~ t~ : ~;. _ _ .. ' ' :' ~1 ~

.., , :. :: ~ .

,: -, ::
'~,' ;:.',~:~ :
.',, ~ ,.
: - 2 7 -.; `-.;
.

In the belt 9, ~he intermediate reinforcing layer 8 constituting the belt layer 3B is composed of 1 rubberized fa~ric containing a bundle of 5 helically formed steel fila-ments each having a filament diameter ~ of 0.25 mm, average diameter D of an outer contour projected on a plane perpen-dicular to the axial direction of one pitch o-f the Ei.lament of 0.95 mm9 ~ =1.25, D~=3.8 and pitch of 10.5 mm. The number of the reinforcing filaments per 25 mm of the rubber-ized fabric is 10. These reinforcing elements are inclined toward le~t a~ 20 with respect to the circumferential direction of the tire. In the present example, the rein-forcing element composed of the bundle of 5 helically formed filaments has a tensile breaking strength of 70 kg/bundle, elongation at tensile breaking strength of 5.5% and modulus o~ elasticity of 1,800 kg/mm2. ~.
The rubber sheet used for covering the belt 9 has ~:
a Shore A hardness of 78, elongation at tensile breaking strength of 350%~ 300% modulus of elasticity of 170 kg/cm2. .~ ~
In order to ascertain the ability of the tire ~ -.
; 20 according to the invention~ provision was made of a tire to be compared A having the same construction as the tire according to the present example, but in which the above mentioned intermediate reinforcing layer 8 is absent and another tire to be compared B having the same construction as the tire according to the present example, but in which the above mentioned intermediate reinforcing layer 8 is replaced by the conventional steel cord, i.e. the steel cord .
; whose construction is the same as the belt layer lB. Then, interlayer shearing strain at the belt end of each of these :~
three tires was measured.
' ' -' - -~

:- . , ~ - , - , . , :
. ., , . ~ ~ , ~, .:, .

!~ In Fig. 9A is shown the interlayer shearing strain at the belt end thus measured o-f each of these three tires when the internal pressure of 6.7 kg/cmZ was applied under load of 2.4 ton.
As seen from Fig. 9A, the maximum shearing strain occurs betwaen the belt layers 2B and 3B. It has been proved ~; ~hat the interlayer shearing strain of the tire acçording ~ , to the invention is smaller than those o-f the comparative tires by 35%.
.
In addition, in order to ascertain the durability o-f these tires, these tires were subjected to an indoor drum test. This test is o a belt endurance test in which provision is made of a steel drum having a diameter of 1.7 m and the tires to be tested inflated by applying an internal -pressure of 6.7 kg/cm2 and driven at a constant speed of 60 km/hour are urged against the steel drum under loads o-f JIS 40% and JIS 50% applied in a step up manner. The results ;~
, .
j of the test are shown in the following Table. ~
.

Table Comparative Tire A 5,300 kr 2~.aAd 3L Separation Comparative Tire B 7,600 km Between occurs Tire according 9 800 k ~etween Local breakage '~ to~the invention . m 2B and 3B occurs ~ As seen from the above Table, the invention is ... .
capable of improving the durability of the tira.

~ 29 -:: .,' '.~ ~:
, . :
'.~: ' ~

, ~ ,,, ~ , . .

. . :

~3 Example 2 In Fig. 10 is shown ano~her embodiment o-f the tire according to the invention. In the present embodiment, the intermediate reinforcing layer 8 composed of helically formed filament shown in Fig. 9 is divided into two inter-mediate reinforcing layer sections 8a, 8b and these sections are arranged near the belt ends, respectively.
These sections 8a, 8b are spaced apart from each other at the crown center by 80 mm and each has a width of 35 mm. As a result, these sections 8a, 8b are extended over a width of 150 mm.
The maximum interlayer shearing strain occurs at the belt ends so that the intermediate reinforcing layer ; sections 8a, 8b are inserted between the belt ends so as to reduce the interlayer shearing strain subjected thereto.
The use of the measures described provides the ad~antage that it is possible to prevent the interlayer shearing ; strain while bringing down the manufacturing cost of the tire.
' 20 Example 3 .~ - . .In Fig. 11 is shown a further modified embodiment of the tire according to the invention. In the present embodiment, use is made of 2 intermediate reinforcing layers 8', 8".
25~ The belt 9 is composed of 4 layers lB, 2B, 3B and 4B arranged in the order as mentioned from the carcass side.
.
Each o~ the cords of the belt layers lB, 4B is formed of the -~
conventional steel cord and has a tensile breaking strength ~ o 188 kg/cord and elongation at tensile breaking strength ; 30 of 3%. The cords of the belt layers lB, 4B are inclined at ' ' :

- .,, ~ .
.' :

. :

~ . , , - , . ~, ~: ; , 20 toward right and 20 toward left with respec~ to the circumferential direction of the tire. The intermediate reinforcing layers 8', 8" correspond to the belt layers 2B, 3B9 respectively, and each composed of a rubberized rein- ~ -forcing element formed o-f 5 helically formed filaments each having a filament diameter ~ o-f 0.25 mm, average diameter D
of an outer contour projected on a plane perpendicular to the axial direction of one pitch of the :Eilament o 0.95 mm, ~ =1.25, D~_3.8 and pitch of 10.5 mm. The reinforcing element has a tensile breaking strength of 70 kg/element, - ~;
elongation at tensile breaking strength of 5.5% and modulus of elasticity of 1,800 kg/mm2. The reinforcing element in the belt layer 2B is inclined at 20 toward right with respec~ to the circumferential direction of the tire and the reinforcing element in the belt layer 3B is inclined at 20 toward left with respect to the circumferential direction of the tire.
As a result, the tire reinforcing elements in the intermediate reinforcing layers 8'~ 8" can absorb the inter-layer shearing strain produced between the belt layers lB
and 4B. In the present embodlment, the coating rubber used -for the belt layers lB, 4B has a Shore A hardness of 78~
elongation at tensile breaking strength of 350% and 300%
modulus of elasticity of 170 kg/cm2~ while the coating ;~
:!:
`~ 25 rubber used for the belt layers 2B, 3B has a Shore A hardness of 67, elongation at tensile breaking strength of 430% and 300% modulus of elasticity of 134 kg/cm2 and hence can easily absorb deformation of the belt 9.
Example 4 In Fig. 12 is shown a still further embodiment of ~'~ , :., ,~`, , , , , , : - ~ .
.
-, ~ , .. . .... .. .

the tire according to the invention. In the present embodi-ment, the 2 intermediate reinforcing layers shown in Fig. 11 are used such that these layers e~fectively function at the belt ends where the maximum interlayer shearing strain occurs.
In the present embodiment, the intermediate .: .
reinforcing layer 8 shown in Fig. 9 is divided into two seckions 8a', 8b'. These sections are spaced apart from . each other and bent at both belt ends with ben~ ends opposed . .
: 10 with each other.
: The reinforcing element constituting each of these . sections 8a', 8b' is composed of a bundle of 5 helically . formed filaments each having a filamen~ diameter ~ of 0.25 mm, average diameter D of an outer contour projected on a plane perpendicular to the axial direction of one pitch of ~ -the fi.lament of 0.95 mm, DmaXin-1.25, D~_3 8 and pitch of . 10.5 mm.
The reinforclng element composed of bundle of 5 .:.
helically formed filaments has a tensile breaking strength of 70 kg/bundle, elongation at tensile breaking strength of 5.5~, and modulus of elasticity of 1,800 kg/mm2. The rein-forcing element in each of these sections 8a', 8b' is ..
inclined at 20 with respect to the circumferential direction ~::
of:~the tire. Each of these sections 8a', 8b' is formed by ~bending an intermediate reinforcing layer having a width of ~; 70 mm in a way such that there is produced a step having a : ;
width of ln mm between the bent ends. The reinforcing ;`~
element in each of these sections 8a', 8b' is extended in the~same direction as the cords in the main layer of the :
belt 9. The use of such benk sections 8a', 8b' makes it .. , ~ ~ .

~ '7 possible tO not only eliminate the interlayer shearing strain produced at the ends o-f the intermediate reinforcing layer but also make occurrence of the interlayer shearing strain between the intermediate reinforcing layer and the main belt layer di-f-ficult. The use of such bent sections 8a', 8b' as well as the helically formed filament ensures a significant improvement of the durability of the belt.
Example 5 In Fig. 13 is shown another embodiment of the tire according to the invention which is applied to a belt construction of a radial tire for construction vehicles.
In the present embodiment, a bel~ 9 is composed of 5 layers lB, 2B, 3B, 4B and 5B in the o~^der as mentioned i from the carcass side and having constructions shown in the following Table.
, .
~' Table _ Tensile Elongation ~ -_ Kind strength ;br~}i~ r lB Bundle of helically 170 kg/bundle 7% toward right _ . .......
2~B Steel cord 560 kg/cord 3.3% toward right _ _ _ _ 3B formed filaments 170 kg/bundle 7% toward left _ 21 4B Steel cord 560 kg/cord 3.3% toward leEt SB formed filaments 170 kg~bundle 7% toward right . _ _ : .

~... . .. .. . . . .

In the belt 9, each of the intermediate rein~orc-ing layers lB, 3~, 5B is composed of 1 rubberized fabric containing a bundle of 21 helically formed steel filaments each having a filament diameter ~ of 0.23 mm, average diameter D of an outer contour projected on a plane perpendicular to the axial direction of one pitch of ~he -filament of 2.07 mm, =1.5, ~=9.O and pitch o-f 11.7 mm. It has been -found out that the belt construction as described above signiicantly exhibits the characteristics inherent to the helically formed steel filament. That is, the intermediate reinforc-; ing layer 3B fllnctions to reduce the interlayer shearing strain, the intermediate reinforcing layer lB functions to eliminate the carcass wave and belt wave and the intermediate reinforcing layer 5B functions to prevent separation faiIure due to cuts subjected to the tread. ~ ~;
As can be seen from the various embodiments ~ described above, the inventors have discovered that the use j of the helically formed -filament as the intermediate rein-. . ::
forcing layer ensures an unexpected résult which reads as follows.
; That is, the intermediate reinforcing layer containing a bundle or bundles of hellcally formed filaments ; assembled together without twisting at random with the ~` adjacent filaments curled in different directions is sand-wlched between the cord layers and hence the intermediate ~reinforcing layer functions to exhibit so-called honeycomb ~ ~ effect. As a result, the intermediate reinforcing layer i~ enables the production of tires which are light in weight (~ and have excellent rigidity.

'`, : ;'"
`.'~
. ~, ', :, . :
. -, , . , . . , .
...... .. .

`'', ' '', ,:

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. In a pneumatic radial tire comprising a reinforcing belt layer including helically formed filaments, comprising a carcass including cords arranged in parallel or substan-tially parallel with the vertical center section through the rotational axis of the tire and a belt interposed between said carcass and a tread and including at least two main layers having cords formed of inextensible material such as a steel cord, etc., said cords being inclined at a small angle along two directions crossed with respect to the circumferential direction of the tire, the improvement comprising an intermediate reinforcing layer interposed between said main belt layers and composed of at least one rubberized layer including reinforcing elements spaced apart from each other and embedded therein, said reinforcing element being formed of a helically formed filament or a bundle of a plurality of helically formed filaments each formed of material having a tensile breaking strength of at least 140 kg/mm2, said reinforcing element having an elongation at tensile breaking strength of at least 1.2 times the smallest elongation at tensile breaking strength of the cords of said main belt layers, said intermediate reinforcing layer as a whole being extensible and compressible.

2. The pneumatic radial tire according to claim 1, wherein said helically formed filament of said reinforcing element has a filament diameter .PHI. of 0.1 to 1.0 mm and average diameter D of an outer contour projected on a plane perpendicular to the axial direction of one pitch of said reinforcing filament, that is, of 2.PHI. to 20.PHI..

3. The pneumatic radial tire according to claim 1, wherein said helically formed filament of said reinforcing element is formed of a steel wire.

4. The pneumatic radial tire according to claim 1, wherein said cord of the main belt layer is inclined at an angle of at most 30° with respect to the circumferential direction of the tire and the said reinforcing element of the intermediate reinforcing layer is inclined at an angle of 15° to 75° with respect to the circumferential direction of the tire.

5. The pneumatic radial tire according to claim 1, wherein said rubberized layer including said reinforcing elements embedded therein is formed of rubber having a Shore A hardness of 50° to 85°, 300% modulus of elasticity of 100 to 250 kg/cm2 and tensile breaking strength of 150 to 250 kg/cm2.